1. Field of the Invention
The present invention relates to a fuel injection system for an internal combustion engine. More particularly, it relates to a fuel injection system applied to an engine in which the cylinders are divided into two groups, and in which each group of cylinders has a phase separated by 360 degrees of crankshaft angle (CA).
2. Description of the Related Art
Known in the prior art is a fuel injection system for an internal combustion engine wherein the cylinders having a phase separated by 360 degrees CA are grouped, and fuel injections are independently attained between the groups. The injection for each of the groups is effected synchronously with the each of intake strokes of cylinders in the respective groups. This means that two injections are attained, for each of the groups of injectors, during one engine cycle corresponding to 720 degrees CA. In order to correct a change in the amount of fuel induced by a change in the engine conditions, such as acceleration or deceleration, a difference in the values of the basic amount of fuel for two consecutive injections calculated for every injection timing is calculated, to determine whether or not the correction should be attained. If the difference is larger than a predetermined value, the correction is attained by multiplying a correction factor, varied in accordance with the degree of acceleration, by the basic fuel amount to obtain the final fuel injection amount.
The basic idea of the prior art is that the correction of the fuel amount is effected upon detection of a difference in the values of the basic fuel amount between the consecutive injections which is larger than the predetermined value. Therefore, a correction is not attained when the difference between the consecutive values of the basic amount is lower than the predetermined value, causing the amount of fuel actually injected to be different from the value of the amount of fuel actually required by the engine. If the predetermined value is set at a small value, a correction of fuel may be unnecessarily attained during the steady state. Furthermore, in the prior art, the fuel amount correction is attained by multiplying the correction factor by the basic amount. However, this method of correction cannot obtain an appropriate amount of fuel during a transient state of the engine.